The present invention generally relates to master-slave manipulator arm systems, and more particularly to a new rate control system for such master-slave manipulator arms which presents force and moment information to the operator.
In general, manipulator systems are complex servo systems and incorporate humans in the feed-back and command segments of the loop. Such systems are used in environments which are unsafe for the presence of the human operator. For example, manipulator systems have been used in such diverse areas as underwater systems, systems exposed to high nuclear radiation and extra terrestrial systems. In the manipulator system, the human operator element is by far the least predictable element in the servo loop, and a design which minimizes the performance sensitivities to the human operator element variations is the desirable servo configuration.
Most maniptulator arm control systems presently used in industry are the bilateral position mode type and are used for dexterous manipultive tasks requiring force reflection. In one type of bilateral position mode control system, input rate commands are integrated and compared with arm position values. Integrators are incorporated into the system, and gimbal data is secured from the arm in the form of joint angular positions. A characteristic of this system is that forces and torques applied to or by the arm can be held after the controllers have been returned to null. This means that a force build-up in a direction not desired must be nulled by controller commands. If the applied forces and moments are displayed to the operator, the operator can readily and quite accurately null these unwanted forces. To accomplish the manipulative task with this type of system, the operator builds up forces in the direction required while at the same time nulling forces in the other directions. This continued nulling procedure consumes a large portion of the total manipulative task time and therefore greatly contributes to operator fatigue.
Another problem with the bilateral position mode type control system is the tendency to build up error signals which can be come larger than the level corresponding to the maximum force capability of the arm. When this occurs, it is necessary to apply a command to reduce the error signal to where a force change can be detected. During this time, however, the operator had no indication of exactly what is happening, and it becomes relatively easy to loose control of the arm by not knowing immediately what to do to regain control. This problem can be avoided by introducing logic into the control equations such that the error signal could not continue to build up after it reached a maximum level. This solution increases the complexity of the manipulator control system without producing any substantial improvement in the tip precision in the manipulator arm.